Such an interaction prevents the Subunit C from participating in the assembly of the Vacuolar Subcomplex (V0 Subcomplex) that is required for the formation of the mature V-ATPase on the vacuolar membranes [19]. This significantly delays the proteolytic endosomal degradation of the internalized EGFr that eventually recycles to the

plasma membrane. This extend the EGFr lifespan and increases the EGF dependent/EGFr signalling [20, 21] suggesting that the interaction with the subunit C GSK1904529A cell line represent an elective function of E5. Conversely, other authors believe that the impairment of V-ATPase and consequent delayed degradation of internalized EGFr is an indirect result of trafficking disruption MCC950 in vivo and impaired fusion of early EPZ5676 clinical trial endosomes with late acidic endosomes [22, 23]. The pH modulation is very important in the regulation of cell organellar trafficking and function in many cellular strains. In particular intra-melanosomal pH has been indicated as an essential factor for the control of melanin deposition in melanocytes [24]. Melanogenesis is regulated through the modulation of tyrosinase, the rate-limiting enzyme of the melanogenic pathway. Differences in tyrosinase activity of melanocytes from different

skin photo types (Caucasian or Black skin) have been reported [25]. It has also been shown that these differences were not due to variations in tyrosinase abundance or gene activity, but to the regulation of catalytic activity crotamiton of the enzyme [25]. In fact, near neutral melanosomal pH is optimal for human tyrosinase activity and melanogenesis while melanin production is suppressed in Caucasian melanocytes by low melanosomal pH [24]. Accordingly, tyrosinase mRNA and tyrosinase protein are actually present also in amelanotic melanomas, where no tyrosinase activity and no melanin deposition can be detected [26, 27]. The probable reason of the declined catalytic activity in these cells, where tyrosinase is present in a inactive state, is the low internal pH due to elevated V-ATPase activity consequent to elevated glycolysis and extra-cellular

acidification occurring during the metastatic spread. Accordingly, it has been demonstrated that substances that act as selective inhibitors of V-ATPase [28, 29] are able to determine the re-activation of tyrosinase and melanogenesis and melanotic reversion of amelanotic melanomas [26]. In the present work we expressed the HPV 16 E5 protein in two lines of human, tyrosinase-positive, amelanotic melanomas with the aim to examine whether the E5 expression could modulate the melanosomal pH and tyrosinase activity. Here we provide evidence that HPV-16 E5 protein inhibits proton pump, causing alkalinisation of endocellular pH, tyrosinase activation, melanin deposition and modulation of sensitivity to dopamine mimetic drugs.